Van Tuyl Lecture: Richard Palin, Colorado School of Mines
September 19 @ 4:00 pm - 5:00 pm
Richard Palin, Colorado School of Mines, Geology and Geological Engineering Department
Berthoud 241, 4-5PM
Constraining Continental Lithospheric Dynamics using Xenoliths: Case Studies from the Colorado Plateau, USA
Abstract: The causes of Cenozoic uplift of the Colorado Plateau, southwestern USA, are strongly debated, though most hypotheses acknowledge the importance of northwest-directed subduction of the Farallon oceanic plate beneath North America since c. 100 Ma. Considerable insight into the effects of subducted slab–continental lithosphere interaction has been gained by multidisciplinary studies of crustal and mantle xenoliths that occur within diatremes emplaced at c. 30–20 Ma in the Navajo Volcanic Field, Four Corners region. Here, I show the results of recently completed and ongoing research that have provided new insight into the geological mechanisms that operated before, during, and after rapid uplift of the plateau during the Oligocene. In one case study, phase diagram-based thermobarometry performed on lawsonite-bearing mafic eclogite xenoliths provides evidence for low-angle subduction and shear-removal of the subcontinental lithospheric mantle beneath the proto-plateau, which subsequently allowed for asthenospheric upwelling and isostatic rebound of the remaining mass. In a second case study, garnet xenocrysts containing exsolution lamellae of hydrous and anhydrous silicate minerals provide insight into the petrological constitution of the asthenospheric mantle beneath the plateau from which they were exhumed. Together, these new data provide new views on large-scale geodynamics in intraplate environments that can be applied to other anorogenic plateaus worldwide, and have implications for changing tectonic processes through geological time.